Motor cortex stimulation in chronic neuropathic orofacial pain syndromes: a systematic review and meta-analysis

Abstract

Invasive motor Cortex Stimulation (iMCS) was introduced in the 1990's for the treatment of chronic neuropathic orofacial pain (CNOP), although its effectiveness remains doubtful. However, CNOP is known to be a heterogeneous group of orofacial pain disorders, which can lead to different responses to iMCS. Therefore, this paper investigated (1) whether the effectiveness of iMCS is significantly different among different CNOP disorders and (2) whether other confounding factors can be impacting iMCS results in CNOP. A systematic review and meta-analysis using a linear mixed-model was performed. Twenty-three papers were included, totaling 140 CNOP patients. Heterogeneity of the studies showed to be 55.8%. A visual analogue scale (VAS) measured median pain relief of 66.5% (ranging from 0-100%) was found. Linear mixed-model analysis showed that patients suffering from trigeminal neuralgia responded significantly more favorable to iMCS than patients suffering from dysfunctional pain syndromes (p = 0.030). Also, patients suffering from CNOP caused by (supra)nuclear lesions responded marginally significantly better to iMCS than patients suffering from CNOP due to trigeminal nerve lesions (p = 0.049). No other confounding factors were elucidated. This meta-analysis showed that patients suffering from trigeminal neuralgia and patients suffering from (supra)nuclear lesions causing CNOP responded significantly more favorable than others on iMCS. No other confounding factors were found relevant.In the early 1990's, Tsubokawa and his colleagues searched for a new therapy to treat intractable neuropathic pain as other forms of therapies, including continuous deep brain stimulation of thalamic nuclei, only provided satisfactory pain relief in approximately 30% of the cases. For that reason, they started to empirically stimulate various brain regions in animal models for intractable neuropathic pain. During their experiments, they recognized the primary motor cortex as a target that could provide excellent pain relief. Within their experiments, Tsubokawa transected the spinothalamic tract in cats, which led to thalamic hyperactivity and pain-related behavior. By stimulating the primary motor cortex in these cats, it was found that both the hyperactivity was inhibited and the pain-related behavior diminished, indicating an analgesic effect of iMCS in the treated cats. These experimental findings were in line with their subsequent clinical investigations in individuals suffering from intractable neuropathic pain as a consequence of thalamic syndrome 1-5 . Since then, iMCS has been carried out in approximately 700 cases world-wide, yielding highly variable outcomes 1,6-40 . Nevertheless, iMCS has become a last resort neurosurgical therapy for different intractable neuropathic pain syndromes 3-5,14,17,21,26,35,41-44 . In 1993, Meyerson et al. reported for the first time on the use of iMCS in chronic neuropathic orofacial pain (CNOP) as a last resort treatment. They reported that, in a case series of 10 individuals suffering from CNOP...

The non-decussating and decussating trigeminothalamic tracts in humans: A combination of connectome-based tractography and histological validation

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